1. Field of the Invention
The present invention relates to a process for producing sulfur hexafluoride (SF.sub.6). More particularly, it relates to a process for easily producing SF.sub.6 having high purity in a mass production at a low cost.
2. Description of the Prior Art
SF.sub.6 has been used as an insulating material for electric power sources having high voltage and large capacity; electric devices, breakers, a lightening arrester and cables in computer circuits in view of non-toxicity and high insulating property.
Various proposals of a production of SF.sub.6 such as a direct combustion synthesis, an electrolysis etc. have been found. Thus, the direct combustion process has been employed as an industrial process in view of a cost etc.
In the direct combustion process, it is necessary to react sulfur with fluorine gas. The fluorine gas has been usually obtained by an electrolysis of a molten salt of KF.nHF etc. Thus, the cost of electric power is remarkably high. Moreover, in a mass production, it is necessary to operate many electrolytic cells in proportion to the production or to use an electrolytic cell having a large capacity. The scale-up of the process is disadvantageous in view of an equipment area and a cost.
On the other hand, another process which does not require the expensive fluorine gas produced by the electrolysis has been also proposed. For example, SF.sub.5 Cl is produced by reacting NOF.3HF with chlorine gas to produce SF.sub.4 and removing by-products and reacting the purified SF.sub.4 with NOF and chlorine. However, NOF used in the process is remarkably corrosive to impart high corrosive effect in the presence of only small amount of moisture. Thus, an reactor made of expensive anticorrosive substance is needed. The process has not been satisfactory as an industrial process.